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Current Status of a Measurement of HadronicParity Violation in the Capture of Cold Neutrons
on Helium-3
for the n3He Collaboration
Mark McCreaUniversity of Manitoba
2015 CAP Congress
June 18, 2015
Introduction
Motivation
Spallation Neutron Source
Experiment Setup
Ion Chamber Details
Ion Chamber Simulation
n3He Introduction
n3He probes the low energy strong interaction, using the weak
interaction by measuring the parity violating directional asymmetry
in the proton recoil from the reaction
~n +3He → p + T + 765keV
Beam n 3He p
θs,~k
T
The goal of the experiment is to measure the asymmetry to the2× 10−8 level.
Theoretical Motivation
q
q
q
q
g
Strong Interaction
q
q
q
q
Z 0,W±
Weak Interaction
u d d
u d d
udd
udd
?
Uncertain HWI
N
N
N
N
PC
Strong
PV
Weak
π, ρ, ω
DDH Parameterization
DDH Meson Exchange Parameters:
Opv = a1πh
1π + a0
ρh0ρ + a1
ρh1ρ + a2
ρh2ρ + a0
ωh0ω + a1
ωh1ω
A Brief Look at ParityUnder a parity transformation P polar vectors such as themomentum transform as
P(~kn)→ −~kn and P(~kp) = −~kpbut axial vectors, such as the neutron spin, remain unchanged
P(~sn)→ ~sn
Orignal State:
Beam n 3He p
θs,~k
T
Parity Transformed:
Beamn3Hep
θs,~k
T
Spin Flipped:
Beam n 3He p
θs,~k
T
Spallation Neutron Source
I Located at the Oak Ridge National Laboratory (ORNL) inTennessee
I 60 Hertz pulsed spallation sourceI approximately 1010 neutrons/secondI n3He is running at the FnPBI Three 20K liquid hydrogen moderator for cold neutron beam
lines
n3He Schematic Diagram
Biological Shielding
NeutronGuide
C1 C2
M1 SMP RFSF
Collimator
3He Target/Detector
HF Solendoid
n3He Target Chamber
Beam
HVSignal
17 HV Frames with 8 wires each16 signal Frames with 9 wires each
Assembled Frame Stack
I 17 HV frames
I 16 signal frames
I 9 signal wires per frame
I 144 signals to read out
Proton Asymmetry in Chamber
~n +3He → p + T + 765keV
Neutron Proton TritonElectron Collection
A proton and triton asymmetry occur in the chamber but thelonger range of the proton causes its asymmetry to dominate
Target Chamber on Stand
I 4 point adjustable stand
I roll, pitch, height were notindependent
I target electrically isolatedfrom stand
I angle block used for initialalignment
Components on Beamline
First Data from Ion Chamber
Ion Chamber Simulation - Garfield++
Garfield++ is a toolkit for the detailed simulation of particledetectors that use gas and semi-conductors as sensitive medium.
I Gas properties calculated using Magboltz
I Ion Mobility from Data from Atomic Data and Nuclear DataTables 17, 177-210 (1976)
I Signal calculated with Shockley-Ramo Theorem:
i(t) = −qv · Ew (r)
I Ew (r) is a calculated weighting field as though the electrodehad a potential of 1V and everything else is ignored
I Fields and Electrode locations from Gmsh and Elmer
I Looking at charge collection times and signals
Geometry - Gmsh
Geometry - Gmsh
Fields - Elmer FEM
Initial Simulation Details
I 200 events at 6 locationsspaced evenly between HVand Signal wire
I ion and electronpropagated from each point
I collection time to becompared with measuredvalues
Collection Times
t(ns)0 500 1000 1500 2000 2500 3000 3500 40000
20
40
60
80
100
120
Electron Collection Times
I Six equally spaced starting positions gave 6 peaks.
I 200 electrons per positions
Integrated Signal - electron
hIntegratedSig-e-0
Entries 200Mean -22.85RMS 0.7114
-610×fC-25 -24 -23 -22 -21 -20
0
5
10
15
20
25 hIntegratedSig-e-0
Entries 200Mean -22.85RMS 0.7114
hist Integrated Signal e -0hIntegratedSig-e-1
Entries 200Mean -71.36RMS 1.393
-610×fC-74 -72 -70 -68 -66
0
2
4
6
8
10
12
14
16
hIntegratedSig-e-1
Entries 200Mean -71.36RMS 1.393
hist Integrated Signal e -1hIntegratedSig-e-2
Entries 200Mean -108.7RMS 2.172
-610×fC-114 -112 -110 -108 -106 -104 -102
0
2
4
6
8
10
12
14
16hIntegratedSig-e-2
Entries 200Mean -108.7RMS 2.172
hist Integrated Signal e -2
hIntegratedSig-e-3
Entries 200
Mean -126.5RMS 2.433
-610×fC-132 -130 -128 -126 -124 -122 -120
0
2
4
6
8
10
12
14hIntegratedSig-e-3
Entries 200
Mean -126.5RMS 2.433
hist Integrated Signal e -3hIntegratedSig-e-4
Entries 200Mean -140.2
RMS 2.506
-610×fC-146 -144 -142 -140 -138 -136 -134
0
2
4
6
8
10
12hIntegratedSig-e-4
Entries 200Mean -140.2
RMS 2.506
hist Integrated Signal e -4hIntegratedSig-e-5
Entries 200Mean -149.4RMS 27.27
-610×fC-150 -100 -50 0
0
20
40
60
80
100
hIntegratedSig-e-5
Entries 200Mean -149.4RMS 27.27
hist Integrated Signal e -5
Ion/Electron pair signals measure from 6 positions
Summary
I Target chamber assembled and tested November 2014
I Target chamber installed December 2014
I First Data from Chamber January 2015
I Data taking to continue until end of 2015
I Charge collection simulations are progressing
n3He Collaboration
Duke University, TriangleUniversities NuclearLaboratory
I Pil-Neo Seo
Istituto Nazionale diFisica Nucleare, Sezionedi Pisa
I Michele Viviani
Oak Ridge NationalLaboratory
I Seppo Penttila
I David Bowman
I Vince Cianciolo
I Jack Thomison
I Paul Mueller
University of Kentucky
I Chris Crawford
I Latiful Kabir
I Aaron Sprow
Western KentuckyUniversity
I Ivan Novikov
University of Manitoba
I Michael Gericke
I Mark McCrea
I Carlos Olguin
Universidad NacionalAutonoma de Mexico
I Libertad Baron
I Jose Favela
University of NewHampshire
I John Calarco
University of SouthCarolina
I Vladimir Gudkov
I Matthias Schindler
I Young-Ho Song
University of Tennessee
I Noah Birge
I Chris Coppola
I Nadia Fomin
I Connor Gautham
I Geoff Greene
I Irakli Garishvili
I Chris Hayes
I Serpil Kucuker
I Eric Plemons
I Mae Scott
University of Tennesseeat Chattanooga
I Josh Hamblen
I Jeremy Watts
University of Virginia
I S. Baessler